LINEAR CONTROL SYSTEMS Ali Karimpour Associate Professor Ferdowsi University of Mashhad

lecture 5 Ali Karimpour Feb Lecture 5 Topics to be covered include: v Nonlinear systems v Linearization of nonlinear systems v Transfer function representation u Property u Poles and zeros and their physical meaning u SISO and MIMO u Open loop and closed loop system u Effect of feedback u Characteristic equation for SISO system

lecture 5 Ali Karimpour Feb Nonlinear systems. Although almost every real system includes nonlinear features, many systems can be reasonably described, at least within certain operating ranges, by linear models. سیستمهای غیر خطی گرچه تقریبا تمام سیستمهای واقعی دارای رفتار غیر خطی هستند، بسیاری از سیستمها را می توان حداقل در یک رنج کاری خاص خطی نمود.

lecture 5 Ali Karimpour Feb Nonlinear systems. سیستمهای غیر خطی Say that {x Q (t), u Q (t), y Q (t)} is a given set of trajectories that satisfy the above equations, so we have

lecture 5 Ali Karimpour Feb Linearized system سیستم خطی شده

lecture 5 Ali Karimpour Feb Example 1 Consider a continuous time system with true model given by Assume that the input u(t) fluctuates around u = 2. Find an operating point with u Q = 2 and a linearized model around it. Operating point:

lecture 5 Ali Karimpour Feb Example 1 (Continue) Operating point:

lecture 5 Ali Karimpour Feb Simulation شبیه سازی

lecture 5 Ali Karimpour Feb Example 2 (Pendulum) Find the linear model around equilibrium point. θ l u mg Remark: There is also another equilibrium point at x 2 =u=0, x 1 =π

lecture 5 Ali Karimpour Feb Example 3 Suppose electromagnetic force is i 2 /y and find linearzed model around y=y 0 M y Equilibrium point:

lecture 5 Ali Karimpour Feb Example 3 Suppose electromagnetic force is i 2 /y and find linearzed model around y=y 0 M y Equilibrium point:

lecture 5 Ali Karimpour Feb Example 4 Consider the following nonlinear system. Suppose u(t)=0 and initial condition is x 10 =x 20 =1. Find the linearized system around response of system.

lecture 5 Ali Karimpour Feb Linear model for time delay Pade approximation s s     

lecture 5 Ali Karimpour Feb Example 5(Inverted pendulum) Figure 3.5: Inverted pendulum In Figure 3.5, we have used the following notation: y(t) - distance from some reference point  (t) - angle of pendulum M - mass of cart m - mass of pendulum (assumed concentrated at tip) l- length of pendulum f(t) - forces applied to pendulum مثال 5 پاندول معکوس

lecture 5 Ali Karimpour Feb Example of an Inverted Pendulum

lecture 5 Ali Karimpour Feb Nonlinear model Application of Newtonian physics to this system leads to the following model: where m = (M/m)

lecture 5 Ali Karimpour Feb Linear model This is a linear state space model in which A, B and C are:

lecture 5 Ali Karimpour Feb TF model properties خواص مدل تابع انتقال 1- It is available just for linear time invariant systems. (LTI) 2- It is derived by zero initial condition. 3- It just shows the relation between input and output so it may lose some information. 4- It is just dependent on the structure of system and it is independent to the input value and type. 5- It can be used to show delay systems but SS can not.

lecture 5 Ali Karimpour Feb Poles of Transfer function قطب تابع انتقال Pole: s=p is a value of s that the absolute value of TF is infinite. How to find it? Transfer function Let d(s)=0 and find the roots Why is it important? It shows the behavior of the system. Why?????

lecture 5 Ali Karimpour Feb Example 6 S 2 +5s+6=0  p 1 = -2, p 2 =-3 Transfer function roots([1 5 6]) p 1 = -2, p 2 =-3 Poles and their physical meaning قطبها و خواص فیریکی آنها

lecture 5 Ali Karimpour Feb Example 6 (Continue) Transfer function step([1 6],[1 5 6])

lecture 5 Ali Karimpour Feb Zeros of Transfer function صفر تابع انتقال Zero: s=z is a value of s that the absolute value of TF is zero. Who to find it? Transfer function Let n(s)=0 and find the roots Why is it important? It also shows the behavior of system. Why?????

lecture 5 Ali Karimpour Feb Example 7 Transfer functions z 1 = -6 z 2 =-0.6 Zeros and their physical meaning صفرها و خواص فیریکی آنها

lecture 5 Ali Karimpour Feb Example 7 Transfer function step([1 6],[1 5 6]) ;hold on;step([10 6],[1 5 6]) Zeros and their physical meaning صفرها و خواص فیریکی آنها

lecture 5 Ali Karimpour Feb Example 8 Zeros and its physical meaning Transfer function of the system is: It has a zero at z=-1 What does it mean? u=e -1t and suitable y 0 and y ’ 0 leads to y(t)=0 صفرها و خواص فیریکی آنها

lecture 5 Ali Karimpour Feb Open loop and closed loop systems Open loop Closed loop Controller سیستمهای حلقه باز و حلقه بسته

lecture 5 Ali Karimpour Feb When is the open loop representation applicable? v The model on which the design of the controller has been based is a very good representation of the plant, v The model must be stable, and v Disturbances and initial conditions are negligible. در چه شرایطی کنترل حلقه باز مناسب است؟

lecture 5 Ali Karimpour Feb SISO and MIMO سیستم تک ورودی تک خروجی و چند ورودی چند خروجی System u1u1 y1y1 SISO u1u1 u2u2 u3u3 y1y1 y2y2 y3y3 MIMO System

lecture 5 Ali Karimpour Feb Sensitivity حساسیت Sensitivity is defined as: M is the system + controller transfer function G is the system transfer function

lecture 5 Ali Karimpour Feb Sensitivity حساسیت G(s) K(s) Open loop system r c G(s) K(s) + - r c Closed loop system

lecture 5 Ali Karimpour Feb Feedback properties ویژگیهای فیدبک Feedback can effect: a) system gain b)system stability c) system sensitivity d) noise and disturbance

lecture 5 Ali Karimpour Feb Exercises 5-1 Find the poles and zeros of following system. 5-2 Is it possible to apply a nonzero input to the following system for t>0, but the output be zero for t>0? Show it. 5-3 Find the step response of following system. 5-4 Find the step response of following system for a=1,3,6 and Find the linear model of system in example 2 around x2=u=0, x1=π